54664-13-0Relevant academic research and scientific papers
Synthesis and X-Ray Crystal Structure of (1S,3R,4S,1'S)-4-Methyl-3-triphenylphosphonium-1--2-hydrido-2-borazetidinium Bromide - the First Example of a Four-membered Heterocycle
Booth, Brian L.,Lawrence, Nicholas J.,Pritchard, Robin G.,Rashid, Humayan S.
, p. 287 - 290 (1995)
The title compound and related derivatives are synthesised from enamino(triphenyl)phosphonium salts and borane, and converted into β-aminophosphonium salts and β-aminophosphine oxides containing two chiral centres.
Synthesis of chiral β-aminophosphine oxides via novel azaboretidinium bromide salts
Booth, Brian L.,Lawrence, Nicholas J.,Rashid, Humayan S.
, p. 3509 - 3518 (2007/10/03)
The enamino(triphenyl)phosphonium salts [Ph3PCH=CMeNR1R2]+ Br- [where R1 = R2 = (CH2)4, (CH2)5; (S)-CHMePh; R1 = H, R2 = (S)-CHMePh; R1 = H, R2 = (S)-(CH2)3-CH(CH2OH)] have been synthesised and have been shown to react with an excess of borane-tetrahydrofuran to give novel azaboretidinium salts - the first examples of four-membered C-B-N-C heterocycles. The structure of [(1S,3R,4S,1'S)-4-methyl-1-(1-phenylethyl)-1,2-azaboretidin-1-ium-2-uid-3-yl] triphenylphosphonium bromide has been established by X-ray crystallography. Borane does not result in any significant stereoselectivity in these reductions and the azaboretidinium salts are mixtures of diastereomers. In contrast, the similar reduction with (R)-(+)-monoisopinocampheylborane or (S)-(-)-monoisopinocampheylborane leads to single diastereomers in high yields when R1 and R2 are non-bulky; with sterically demanding groups the azaboretidinium salts are unstable and decompose on work-up. Heating these azaboretidinium salts with aqueous sodium hydroxide in methanol, or better, aqueous sodium hydroxide alone, results in the direct formation of the phosphine oxides, Ph2P(O)CH2CHMeNR1R2 which, in the case of compounds derived from IpC2BH2, have an ee value of >75%. In some cases, particularly when R1 and R2 are bulky, the use of sodium hydroxide in methanol results in an appreciable amount of rac-Ph2PCH2CHMe(OMe) as a by-product, but this can be avoided by carrying out the reactions in the absence of methanol.
